AWeber requires a private app to be created on their Labs site, before external systems can interact with your AWeber account.
Please make sure that you have followed these steps:
1. Go to Aweber Labs, create a new account there and create private app.
2. Go to settings of that private app and copy 'Consumer Key' and 'Consumer Secret' and enter them in the appropriate fields in Leadifly.
3. Copy 'List ID' from your AWeber account (only numbers part), enter it in to the appropriate field in Leadifly and click Save Changes.
4. Now you need to give permission to this newly created app to access your AWeber account. Click the link in the Leadifly control panel to authorize it.
5. If everything went well, the Code value should be not empty.
6. The final step is to verify this code and get your Access Token and Access Secret. Click the link in the Leadifly control panel to do this.
If this doesn't work, please repeat steps 4,5 and 6. After you save your new credentials, click the Validate Settings button, if it is visible.
Also to use AWeber, please make sure that you have selected 'Use Aweber' on the Leadifly AWeber tab.